1. Field of the Invention
This invention pertains generally to plant husbandry, and more particularly to methods and compositions having utility in potato treatment.
2. Description of the Related Art
Potatoes have origins that have been documented as early as 7,000 years ago. This seemingly simple crop existed for thousands of years unknown to Europeans, in the Andean region of South America. However, once the first potatoes were exported to Europe, they were rapidly and extensively adopted as a staple food crop. Some individuals claim the potato was the most valuable commodity discovered in the new world.
The extent of adoption, and the importance of farming practices, is perhaps best illustrated by the Irish potato famine which occurred in 1845 to 1849. The potato had become so vital to society, as such an abundant and low-cost staple, that there was an associated increase in population and even greater dependence upon the potato. The introduction of the disease late blight, combined with an unstable political situation, is associated with the starvation of one million Irish and the emigration of another two million. This large number of deaths and emigration is of a magnitude more frequently thought of as being associated with World Wars than with food supplies of the time period.
Today, potatoes rank fourth among all food crops in total production, behind rice, wheat, and corn. In 2002, the United States, which is the fifth-highest producer world-wide, sold forty billion pounds of potatoes for approximately 2.8 billion dollars. Consequently, potato farming practices and disease control have been and remain very vital to modern civilization. Any practices which can improve upon existing technologies are of great economic importance.
One practice which is commonly associated with potatoes is the generation of potato seed pieces prior to planting. The majority of farmers in the Western and Midwestern United States plant potato seed pieces rather than whole potatoes. A recommended practice is to select potato seed tubers weighing between 3.5 and 10 ounces. For most varieties the tubers are cut into seed pieces weighing from 1.5 to 2.5 ounces, each of which are generally capable of producing new potato plants.
When freshly cut, the potato is more susceptible to disease, since there is no skin on the cut to provide protection. While it is possible to directly plant these potatoes, without a protective skin yields will be undesirably reduced. Instead, in a process called suberization, the cut is allowed to heal prior to planting in a way which will improve yields. The healing involves the deposition of a complex fat-based compound called suberin in the outer two or three layers of intact cells. This suberin layer protects the surface from pathogens, and reduces moisture loss. Eventually a new layer called the phellem layer is developed and becomes suberized, ultimately forming a barrier comparable to the skin of the potato.
The initial suberization is competed in two to four days, but the formation of the phellem layer may require one to two weeks. Unfortunately, as already noted, until suberization is completed, the seed pieces are more vulnerable to pathogens. To prevent undesirable rot and decay during the suberization process, cutting knives and associated equipment are preferably kept in a relatively sterile condition by careful cleaning and sanitation with suitable disinfectants. However, once cut and exposed to air and airborne pathogens, the tuber surface is still vulnerable.
To reduce or prevent disease from developing in the cut tuber piece, freshly cut surfaces of the tubers are most preferably treated with fungicide dust. The dust will help to protect the tuber until a new barrier can be established by suberization. Seed pieces may be stored for 10 to 14 days while a new wound barrier tissue or phellem layer develops over the cut surface, or planted within about five days of cutting, after the initial suberization (cut-and-plant). In some cases, a liquid pesticide is sprayed on the seed pieces and then a powder is added to control excess liquid and promote drying of the surface. Application of a pesticide treatment may also be advantageous when whole, uncut, tubers are used for planting (single-drop).
The fungicidal dust can include active ingredients for preventing fungi or other opportunistic organisms including mold, insects and bacteria from negatively affecting the seed pieces prior to planting while the fresh cut seed pieces are drying and forming a barrier tissue and after planting prior to and during sprouting. Active ingredients may include insecticides, fungicides, and herbicides or other pesticides; as well as surfactants, nutrients, pigments and fertilizers; or other materials based on the intended action. Active ingredients are typically highly concentrated so they are commonly attached to a carrier and diluted with a diluent. A carrier is a substance impregnated with the active ingredient, whereas the diluent dilutes the active ingredient.
The other ingredients besides the active ingredients are sometimes referred to as ‘inert ingredients’ although this language is losing appeal since rarely is an ingredient completely inert. The other ingredients typically include relatively benign materials used for a “carrier” and/or a “diluent.” Many powdered pesticides require that active ingredients be applied at very low rates per unit of area, but active ingredients as manufactured are highly concentrated so dilution is required from a carrier or diluent. For liquid pesticides, water is the chief diluent, but dry pesticides require other materials. A dry carrier, sometimes referred to as a dry diluent, or simply “diluent”, is used with dry pesticides to dilute the active ingredient. If the active ingredient is impregnated on a carrier, then the carrier with active ingredient can be incorporated in a diluent. In some cases, the active ingredient can be incorporated directly into the diluent. The diluent and often the carrier may comprise a variety of materials, such as talc, zeolites, and wood flour, and the diluent and carrier may even be of the same composition.
Powdered materials are used in many commercial processes and products. Powder manufacturing, handling and end-use often generates undesirable airborne dust, referred to as “fugitive dust”, which is a leading environmental contaminant that commonly poses health risks, particularly to those individuals employed in proximity. Background information can be found in the following articles, each which are hereby incorporated by reference:    Bohl, William H., Nora Olsen, Stephen L. Love and Phillip Nolte. 2003. Seed and Planting Management. Pp. 91-107 In Jeffrey C. Stark and Stephen L. Love, Potato Production Systems, University of Idaho Agricultural Communications. ISBN 1-58803-001-6.    Gill, Thomas E., Ted M. Zobeck, John E. Stout, and James M. Gregory. 1997. Fugitive dust generation in the laboratory. Wind Erosion: An International Symposium/Workshop. Manhattan, Kans. 3-5 June.    International Union of Pure and Applied Chemistry (IUPAC). 1990. Glossary of Atmospheric Chemistry Terms. See Calvert, Jack G. Pure and Applied Chemistry, 62(11):2167-2219.    World Health Organization. 1999. Hazard Prevention and Control in the Work Environment: Airborne Dust. WHO/SDE/OEH/99.14.
“Dust” is defined by the International Union of Pure and Applied Chemists (IUPAC, 1990) as “small, dry, solid particles projected into the air by natural forces, such as wind, volcanic eruption, and by mechanical or manmade processes such as crushing, grinding, milling, drilling, demolition, shoveling, conveying, screening, bagging and sweeping. Dust particles are usually in the size range from about 1 to 100 microns in diameter, and they settle slowly under the influence of gravity.” The International Standardization Organization (ISO 4225-ISO, 1994) modifies the definition to refer to particles less than 75 microns in diameter.
The World Health Organization (WHO) notes that particle diameter does not fully explain how the particle behaves in its airborne state and defines the particle aerodynamic diameter as “the diameter of a hypothetical sphere of density 1 g/cm3 having the same terminal settling velocity in calm air as the particle in question, regardless of its geometric size, shape and true density (WHO, 1999). WHO further defines the following fractions for health-related measurement. The “inhalable fraction” is hazardous when deposited anywhere in the respiratory tract. The “thoracic fraction” is hazardous when deposited anywhere within the lung airways including the gas-exchange region. And, the “respirable fraction” is hazardous when deposited anywhere in the gas-exchange region. Respirable dust is generally described as the fraction below four (4) microns. However, standard fractions are often taken at below ten microns and below two and one-half (2.5) microns.
Dry pesticides are known to release dust into the air when manufactured, handled or when applied, creating a potential health concern for manufacturers, handlers and applicators. In most cases, a person is needed to apply the pesticide but the respirable dust is a serious and undesirable health concern. Reducing airborne respirable dust is therefore highly desirable.
An example of a material that generates respirable dust is a fungicide dust used for treatment of potato seed pieces prior to planting. Commercial potato seed treatment product formulations typically include a blend of red alder (Alnus rubra) or Douglas fir (Pseudotsuga menziesii) bark, talc, and zeolite as the diluent materials or carrier. Physical properties of these materials provide acceptable adherence to moist surfaces of cut seed while avoiding coagulating or clumping which can plug application equipment.
Chollet discloses a seed treatment dust in U.S. Pat. Nos. 5,007,953 and 5,024,690, the teachings of each which are incorporated herein by reference, which comprises comminuted alder bark, a diluent material and an active ingredient. Chollet discloses using the seed treatment dust on seeds of grains, legumes, onions, tubers and flowers, and particularly, the dusting of tuber seeds such as potato seeds. However, the use of alder bark is not as efficacious as desired, due to cost, limited supply and because it does not effectively reduce fugitive dust, among other reasons.
U.S. Pat. No. 6,228,883 to Riggs, the teachings which are also incorporated herein by reference, discloses a fungicidal composition comprising a solid or liquid diluent, including carriers, such as talc, zeolites, alder bark, kaolin, diatomaceous earth, mineral oil, water, and the like. Potato seed treatments used in the Riggs' examples were based on a “potato dust inert system” (PDIS) shown in the present Table 1, where three ingredients, talc, zeolite and alder bark comprise 100% of the diluent. The talc identified by Riggs as Cyprus BT-200 is now called Silverline 002 by Luzenac Americas, Inc. The PDIS content, that is diluent content, of the resultant potato seed piece treatment fungicide dust ranged from 89.5% to 94.7% w/w (weight percent). While Riggs may have successfully included alder bark in the diluent, as aforementioned the use of alder bark is not as efficacious as desired, due to cost, limited supply and because it does not effectively reduce fugitive dust, among other reasons.